1. Field of the Invention
The present invention relates generally to the field of preparation of epitaxial thin films of magnetic rare earth garnets by chemical vapor deposition and, in particular, to the use of certain organometallic compounds as the source of the rare earth metals for the chemical vapor deposition.
2. Description of the Prior Art
Epitaxial garnet thin films of rare earths and other metals are utilized for applications in high frequency devices such as microwave devices common in bubble domain memories for the computer industry and magneto-optic devices. In the prior art, several methods have been employed to produce epitaxial garnet thin films of rare earth metals or rare earth metals in combination with transition metals by chemical vapor deposition.
One principle method utilizes rare earth or transition metal halides (normally chlorides) as the starting materials. Examples of this method are found in U.S. Pat. Nos. to Gambino 3,131,082 issued Apr. 28, 1964 and Wehmeier 3,615,168 issued Oct. 26, 1971. While this method has met with some success, it does suffer from several drawbacks one of which is the relatively low vapor pressures exhibited by the compounds which requires relatively high chemical vapor deposition temperatures. For example, the melting point of yttrium chloride(YCl.sub.3) is 721.degree. C. and that of gadolinium chloride(GdCl.sub.3) is 607.degree. C. Thus, in order to achieve any practical chemical vapor deposition rate, very high temperatures (about 1200.degree. C.) must be used.
A further prior art reference describing organometallic compounds is found in a patent to Cais et al. 3,326,948 issued June 20, 1967. That reference illustrates and describes organometallic carbonyl compounds of transition metals and rare earth(lanthanide) metals having cyclic and olefinic constituents. While these compounds do exhibit increased vapor pressures and may be used to reduce the chemical vapor deposition temperature, the preparation of such compounds is a relatively difficult and involved procedure and the handling of the resultant compounds is also difficult.